Regenerative braking is one type of electrical braking procedure. Normally energy is
dissipated in any braking procedure and in most cases, energy is lost as heat.Regenerative braking has been designed to utilize this energy,so the amount of energy lost as heat in other braking processes will be used for some productive purpose in this process.For example, in some areas with lot of mountains, a train is allowed to come down from top of mountain only when another is going up, so that one train can transfer its energy to another.Its charming, na!!
dissipated in any braking procedure and in most cases, energy is lost as heat.Regenerative braking has been designed to utilize this energy,so the amount of energy lost as heat in other braking processes will be used for some productive purpose in this process.For example, in some areas with lot of mountains, a train is allowed to come down from top of mountain only when another is going up, so that one train can transfer its energy to another.Its charming, na!!
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| Fig:Regenerative braking |
Look at the schematic. when we apply braking, stator is of course disconnected from main supply using switch set-4. But the rotor is rotating due to its inertia. In case of DC, synchronous and permanent magnet motor, rotor has distinct flux source. And in case of induction motor, rotor has residual magnetism. Therefore, virtually all machine has some sort of flux source on its rotor. When rotating due to inertia, this flux cuts
stator
windings and produce some voltage and hence power. This power is dissipated in dynamic braking by some resistor. But now we will make an arrangement to convert this power to electricity.That is why we call it regenerative. I assume you understand how transfer of energy may cause break, but if you do not as I did not, you may read my article on reason of DC injection and dynamic braking of electrical machine using resistor.
When switch set-4 is at open position (braking position), switch set-1,switch set-2 and switch set-3 is at closed position. Therefore, voltage induced in the stator side is converted to DC by the rectifier. Then it is conditioned by DC-DC converter. This conditioning is necessary because induced voltage will be varying in magnitude and frequency due to variable speed of rotor, making it necessary to be comparable with
source voltage. Required frequency for supplying this energy is obtained by inverter. This is how we feed main supply the very energy we get from rotating rotor. So rotor is loosing its energy more rapidly and slows down quickly. Hence, braking is implemented.
It is pretty simple concept, but probably a little bit difficult in actual implementation because of the complex controller of DC-DC converter and Inverter. The inverter should be a sine wave voltage source inverter. It may be BJT, MOSFET or IGBT driven. The rectifier may be uncontrolled full wave diode rectifier or controlled SCR or BJT rectifier. Uncontrolled rectifier should be used if simplicity is preferred. Frequency conversion is necessary because we cannot feed source with variable frequency. If we want to give energy back to the source, supplied voltage and current must be of same frequency as the source. Switch set-1,2,3 and 4 may be electromagnetic relay or solid state switch. Solid state switch performs faster than electromechanical relay and may be preferred.
This is all I had to say on regenerative braking, if you find it useful or misinformed or incorrect, please leave a comment. Also, I would highly appreciate if you subscribe to my blog, it will be highly inspiring.
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This is quite helpful
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